Process for catalytic conversion of hydrocarbons



2 Sheets-Sheet 1 l. s. KASSEL.v

Filed Nv. so, 1939 PROCESS FOR CATALYTIC CONVERSION 0F HYDROCARBONS oct. 27, 1942.

oct. 27,1942. L s, KASSEL PROCESS FOR CATALYTIC CONVERSION 0F HYDROCARBONS Filed Nv. 30. 1939. 2 Sheets-Sheet 2 i Patented Oct. 27, 1942l PROCESS FOR CATALYTIC CONVERSION F HYDROCARBON S Louis S. Kassel, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware y Application November 30, 1939, Serial No. 306,935

schim. (ci. 19e-s2) This invention relates to a process for the catalytic conversion of hydrocarbon oils into motor fuels of high antiknock value. More particularly, it concerns the conversion of hydrocarspent for this purpose.' can be used at higher temperatures for producing additional yields of an olefin-containing gasoline.

Eventually the catalysts require regeneration in order to restore activity which has beendecreased largely due to an accumulation ofcarbonaceous or hydrocarbonaceous deposits on their surfaces. In reactivating the catalyticmasses.

temperatures of the order of those employed in VIn one speciilc embodiment the present inven y tionvcomprises a continuous catalytic process for converting normally liquid hydrocarbons into high yields of desirable products including substantially `oleiln-free, high antiknock vdistillate suitable for use in aviation fuel which comprises bon oils of `petroleum origin into substantially 5 converting said hydrocarbons in a plurality of olefin-free gasoline suitable for use as an aviation substantially identical conversion stages serially base fuel. arranged, wherein the flow of hydrocarbons to,

The use of various catalytic masses for the proand withdrawal of reaction products from, the duction of increased yields of high antiknock moentire group of said conversion stages is substantor fuel has been practiced. Under certain contially constant, and lwherein the. repeated seditions of operation involving temperatures in `quence of steps is carried out at each of said excess of approximately 900 F. and relatively conversion stages in a cyclic manner comprising low pressures, gasoline and gases containing large a primary step wherein a stream of hydrocarbon percentages of olefin hydrocarbonsare produced is contacted with freshly reactivated catalytic by the catalytic cracking of hydrocarbon oils material under conditions of' temperature and cf higher than gasoline boiling range. The pressure adequate to effect substantial conversion gasolines produced are of good antiknock value, thereof to substantially olefin-free distillate, a which makes them particularly desirable for use secondary step in which -a separate stream of as motor fuel, I hydrocarbons is contacted with partially spent When such gasolinas are subjected to the -action .20 eetlyst previously Used in Seid primary Step 1111- ot certain catalytic masses at relatively low temder conditions of pressure and relatively higher peratures, e. g., of the order of o-900 F., subtemperature adequate t0 produce substantial stantially olefin-free gasolines are obtained acyielS 0f relatively olcilnic gaS011I1e.atert1ary step companied by little or nochange in the antiin which said catalyst used in said primary and knock value. As a consequence the combinag5 secondary steps is partially reactivated by treattion process offers a good method of producing ment with wilgen-Containing ses at a temperesubstantially saturated gasoline suitable for use ture substantially higher than that used 1n said in aviation fuels, primary step, andsl quaternary step lnwhich The catalytic masses employed in these reacthe reactivation is completed while the catalyst tions comprise particularly the so-called silica- $0 temperature is being restored to that suitable alumina, silica-zirconia, or silica-alumina-zirfOr Said primary Step, recovering the 83S and conia composites made by the separate or simulgasoline formed, returning a, portion of the intaneous precipitation of silica and an oxide of suillciently converted oil for further conversion alumina and/or zirconia under conditions such while maintaining thOSe- CenVerSiOn Stages Operthat alkali metal ions are eliminated. lOther 85 ating in Said, primary and Quaternary Steps in cracking catalysts such as acid-treated clays may heat exchange relationship by means 0f n eiralso be used, although they are not necessarily culating fluid heat exchange medium, and mainexactly equivalent. taining those conversion stages operating in said 'I'he catalysts may be used for producing olesecondary and tertiary steps in heat vexchange 1in-free gasoline, and after being substantially 0 relationship by means of a. separate circulating fluid heat exchange medium.

The two temperature levels may be achieved and maintained by the use of two separate circuits of heat exchange tluidsso arranged that each catalyst region may be brought into heatexchange relationship with the fluid in either circuit. One method of accomplishing this is illustrated in Figure 2, which will be explained in detail later in the specifications. The materials which may be used as heat exchange media include low melting metals or alloysl alkali metal hydroxides,` mixtures of salts melting below 450l 500 F., etc.

' Figure'l is a diagrammatic representation nof one embodiment of the present invention showing a process hook-up involving the use of the various temperature levels contemplated for process and reactiviation and illustrating the cyclic manner in which the various steps are carried out.

Figure 2 is a diagrammatic representation of more briey for the other three.

the heat exchange system which may be usedl in commotion with the process ow illustrated in Figure 1.

Figures 3. to 'I inclusive show the settings of vthe switching valves opposite to the settings shown in Figure 2, and are used in describing the flow of heat exchange media during the various steps of the process cycle. Y

The drawings should not be interpreted as limiting the invention to the exact apparatus or equipment shown since obviously numerous types of reactors or variations of the type shown could be employed. These are understood to be included within the scope of the present invention. The apparatus consists essentially of four or more manifolded reactors together with suitable fractionation, heating, condensing, pumping, etc., equipment. The reactors may comprise any suitfable type, of which thatvillustrated is a simple diagrammatic representation, consisting of one or more catalyst tubes or chambers disposed in a shell through which heat exchange media can be circulated; It should also be understood that the invention may be carried out without the use of the heat exchange media, in which case the reactors will be of somewhat different design since obviously the shells surrounding the tubes or chambers would be dispensed with in this case. Under these circumstances the catalyst tubes or chambers may be insulated or may be enclosed in an externally heated zone.

The entire operation involves a. repeated cycle of four phases. During all of these phases, the ows to and from the entire group of reactors remain the same, but the ilows to and from each separate reactor may change with each change of phase. scribe the ow completely for a single'phase and It is obvious that'the choice of phase to be described first and completely is entirely arbitrary.

Referring to Figure l, the hydrocarbon oil charge is introduced through line 5, valve 0, pump l, and enters coil which is disposed in heater 9. The oil may be heated to a temperature of approximately 90041200" F. and at a pressure of substantially atmospheric to slightly superatmospheric, say of the order of 50-150 pounds per square inch. The oil then passes through line E0 and'valve il to line i2, valve i3 and enters catalyst tube it of reactor 2. The catalyst tube may be surrounded by shell i5 having inlet line i0 and outlet line il through which heat exchange media may be circulated. The reaction products pass through line i0 and valve it) to line and pass thence to fractionator 2l. riihe gaseous fraction which contains olei'lnic hydrocarbons suitable for vconversion into gasoline by polymerization and/or alkylation methods is removed through line 22 and valve 23. Gasoline may be Withdrawn through line 20 and valve 25 to storage, The gasoline produced is of high antiknock value, and is .relatively oleflnic in charn acter, being suitable for use as an automobile fuel. As an alternative, a part or all of the gasoline may be passed through line 20, valve 2l to line 3l for conversion to substantially olenfree distillate suitable for use in aviation motor fuels in a manner which will be described hereinafter.

A residue unsuitable for further conversion may be withdrawn through line 20 and valve 20. Insuiiciently converted oil may be passed through line 30, valve 3i, and pump 'l to be recirculated for further conversion in the process. A higher boiling fraction of naphtha or other side cut material may be withdrawm from fractionator 2l through line 32 and valve 33.

Hydrocarbon oil which may be the same or different from that used in the relatively high temperature step Just described is introduced through line 34, valve 35, pump 36 and line 31 to coil 38 which is disposed in heater 39. The oil is heated to a temperature within therange of approximately o-900 F. and a pressure of approximately 50-1000 pounds per square inch. The heated oil passes through line 40, valve 4I to line 42 and valve 43 into catalyst tube 44 which is disposed in reactor I., Reactor l is similar to reactor 2 and has a shell 45 with inlet 46 and outlet 41 through which heat exchange medium may be circulated. The reaction products are removed through line 48, valve 49 to outlet 50 and It will be sufficient, therefore, to del passed to fractionator 5l.

Gaseous products may be removed through line 52 and valve 53. Substantially saturated gasoline suitable for use in aviation fuel may be removed through line 5t and valve 55. A side-cut of naphtha or higher boiling oil may be removed through line 56 and valve 5l. A residual oil may be withdrawn through line 58 and valve 59. A portion of insulciently converted oil may be recirculated by passing through line 60, valve 6 l valve 32 to line 3l and thus returned to the lower temperature reaction stage for further conversion. Reactivation gases are introduced through line 03, line 6d, valve 35 intoreactor 3 which is similar to reactors i and 2, and c ontains catalyst tube t@ in shell 6l which is equipped with inlet and outlet lines E0 and et. Reactivation during this stage is carried out at a temperature in excess of that used in reactor 2, being normally within the range of S900-1500*o F. and preferably not exceeding approximately V13.50 F. The reactivation gases ,pass through line i0, valve 'il to line it. A portion of them may be recirculated in a manner not shown. Reactivation gases pass from line 03 through line 713, valve it to reactor l which is similar to reactors l, 2 and 3, and contains catalyst tube l5 disposed in shell E0 having inlet and outlet lines lll and 'it for the circula-s tion of heat exchange iluid. The reactivation gases pass through line le and valve t0 to line l2. The temperature in reactor d is restored to the level of reactor i during this step.

After a time governed by .the state of activity of the catalyst in the various reactors, the ows are switched and the next phase of the cycle is begun. ln this case, the heated hydrocarbons from line i0 enter reactor i through line 0l and valve 02, and pass thence through line 03 and valve 00 to line 20 to be disposed or as previously described. At the same time the oil from line @it passes through line 85, valve 00 and reactor i to line 0l, valve 88, line 50 and fractionator iii. Reactivation gases enter reactor from line tati by way of line t@ and valve @0, and are passed to line HZ through line 0l 'and valve 02. The reactivation gases continue to pass through reactor 3 as previously described except that during this phase the temperature in the reactor is being restored to that used for processing in the lower temperature range.

After a suitable interval, the valve settings are changed to those of the third phase of the cycle. In this phase reactor l is being reactivated at the higher temperature, reactor 2 at the lower temperature, reactor 3 is processing` at the lower temperature and reactor t is processing at the higher passed through reactor by way of line 93 and valve .94, and passed thence to line 12 by way of line 95 and valve 96. Reactivation gases continue to pass through reactor 2 as previously described while the temperature is being returned to the level for use in the lower temperature processing step. Oil from line 40 is introduced to reactor 3 through line 91 and valve 93, and is removed through line'99 and valve |00 to line 50 and thence to fractionator 5|. At the same time, oil from line is pased through line |0|, valve |02 to reactor 4 which is operating in the higher temperature range, leaving the reactor through line |03 and valve |04 which joins withline 20 and passes to fractionator 2|.

- range, reactor 3 is processing in the higher temperature range, and reactor 4 is reactivating at the higher temperature. In this case reactivation gases continue to4 pass through reactor as just described while the temperature is being restored to the lower temperature level. Hydrocarbons from line 40 pass to reactor 2 through line |05 and valve |06, passing thence through line |01 and valve |08 to line 50 and then to fractionator `At the same time the oil from line I0 is introduced into reactor 3 through line |09 and valve I0, After conversion in the higher temperature range, the reaction products pass through line and valve ||2 to line 20 and thence to fractionator 2 Reactivation gases during this phase of the cycle are introduced into reactor 4 through line 13 and valve 14, .and lare passed to line 12 by way of line 19 and Valve 90. According to the operation just described, separate streams of hydrocarbon oil are processed under different conditlons of temperature and pressure to produce products of substantially different characteristics, namely, a relatively; oleflnic gasolinel from the high temperature conversion step, and a substantially saturated gasoline from the lower temperature conversion step. Aside from the position of the two conversion steps in the cycle of operation, the higher and lower temperature steps are not related. According -to one alternative, these steps may b e further related in several ways which are about to be described.

According to one alternative, recycle oil from fractionator 2| may be passed through line ||3, valve ||4, line 60 and valve 62 to line 31 where it is combined with the charging stock from line 34 and valve 35 for conversion in the lower temperature step. If so desired, little or no oil need olefin-free gasoline suitable for use in aviation fuel. Although the gasoline may be treated in this manner without the addition of either recycle oil from fractionator 5| or fresh charging stock from line 34, it is also within the scope of the invention to4 add oil from either or both of these sources to the gasoline fraction being treated. Since fractions used for aviation fuel rarely have more than a 300 F. end-point, and since the fraction boiling above 300 F. and having an end-point within the normal gasoline boiling range is of good anti-knock qualities, it is within the scope of the invention to pass a fraction suitable for conversion to aviation fuel through line 24, etc., to the low temperature conversion step,

Vand at the same time withdraw a naphtha fraction as indicated through line 32 use in automobile fuels.

Certain pumps, heat exchangers, condensers, stabilizers and other auxiliary equipment necessary to the operation of such a process have been omitted in the interests of simplifying the drawings.

and valve 33 for Referring to Figure 2, a heat exchange medium which may comprise any suitable liquid material such as mixtures of molten salts, metals or metal alloys and the like, is introduced through line ||5, valve H5, line ||1, pump ||8, and passes through exchanger ||9 wherein it may be heated or cooled as desired. When the medium is first introduced it is heated to the desired reaction temperature. The medium passes through line |20 to switching valve |2| and thence to reactor at the lower temperature range of 50G-900 F.

be charged through line 34, so. that the oil being charged to the lower temperature conversion step comprises essentially or entirely insufficiently converted oil from vfractionators 2| and 5|.

According to another alternative a part or all of the insufficiently converted oil from fractionator 5| may be passed through line 60, valve 6|, line ||3 and valve ||4 to line 30 and thence by previously described routes to the high temperature conversion step. At the same time a part of the oil from line may be passed Ithrough valve 62 to line 31 and'thus be recirculated to the lower temperature conversion step.

According to another alternative which was indicated earlier in the description. a fraction or all of the gasoline from fractionator 2| may be passed through line 24, line 26, valve 21, pump 36 and line 31 to the lower temperature conversion step wherein it is converted to substantially The medium passes through line |275 and switching valve |26, line |21, valve |28, line |29, switching valve |20, line |3| to shell `|32 of reactor 4'. This reactor is similar to reactor and contains catalyst tube |33. In this step of the processing cycle, reactor 4' is being returned from the higher temperature reactivation phase of the cyclel to the lower temperature rreactivation phase at 50G-900 F. The fluid medium passes through line |34, switching valve .|35 to line ||1 where' it is picked up by pump H3 and recirculated. When the system is filled with the heat exchange medium, valve ||6is closed. Line ||5 and valve ||6 may be used as a means of draining the system when the plant is shut down.

Sumcient molten medium to fill the second heat exchange system is introduced through line |36 and valve |31, passing into line |33 and pump |39. The molten mixture passes through exchanger |40 which may be a heater or cooler as is necessary for the particular operation being carried out. The salt passes through switching valve |2|, line 14|, switching valve |26, line |42 to reactor 2', which is similar to reactors and 4' and contains catalyst tube |43 disposed ln shell |44. Reactor 2 is at this point being used in the high temperature processing phase at G-1200" F. The medium leaves reactor 2 through line |45, passes through switching valve |20, line |46 to reactor 3' which is similar to the other catalytic reactors and contains tube |41 disposed in shell |43. Reactor 3' is in the higher temperature reactivation phase of the cycle in the range of 9001500 F. The medium leaves the reactor through line MS, switching valve l30, line |50, switching valve l3'5, returning through line I! to pump E39 whereby it is recirculated.

The switching valves are four-way valves which are set in the positions indicated in Figure 2 when operating as just described. In order to carry out a complete cycle of operation, it is necessary to change the valve settings in order to direct the ow of heat exchange media-to the proper reactors. Figures 3-7, inclusive, show the settings of valves lil, i126, E28, it@ and l opposite to the settings as shown in Figure 2. The lines and valves are numbered to correspond with the numberings in Figure 2 so that these figures could be superimposed on the valves as illustrated in Figure 2 and would correspond in.

every Way except as to the position ofthe switching valve proper. Figures 3-'7 are referred to in order to describe the ovv oi heat exchange media when carrying out the complete cycle oi processing steps previously described in connection with Figure l. According to the valve setting just described in connection with Figure 2, reactor l' is processing at the lower temperature,

- reactor 2' processing at the higher temperature7 reactor il reactivating at the higher temperature, and reactor "i reactivating at the lower temperature.

`when the operation is shifted in the course of the regular cycle so that reactor i' is proceasing at the higher temperature, reactor 2 regenerating at the .higher temperature, reactor 3 regenerating at the lov/er temperature and reactor processing at the lower temperature, the valves are in the following positions: valve ili asin Figure 3; ld as in Figure d; il as in Figure 5; 530 as in Figure E, and 535er, in Figure il.

ln the next regular step in the operation, reactor i is reactivating at the higher temperature,

Figure 2, and valves l26, t28, i3d and H35 as in Figures 4, 5, 6, and 7 respectively.

The cycle is completed when the valvesare' switched to the original position shown in Figure 2 wherein reactor I' is processing at the lower temperature, reactor 2' processing at the higher temperature, reactorl 3f reactivating at the higher temperature, and reactor 4' reactivating at the lower temperature..

The following .example is given to illustrate the usefulness and practicability of the invention but should not be construed as limiting it to the exact conditions, apparatus, catalysts, charging stocks, etc. used therein.

The catalyst used was a silica-alumina-zirconia composite yprepared by precipitating the hydrogels of the various components followed by dry ing, forming into pellets and calcining. A Mid- Continent gas oil was charged to the high temperature step as described in the foregoing specications using a temperature yof 950 F. and a pressure of approximately 50 pounds per square inch. The 400 F. end-point gasolineformed in this way was separated for use as an automobile fuel. The C3 and C4 oleflns contained in the gas were polymerized to form additional yields of high octane number motor fuel using a solid phosphoric acid catalyst made by reacting liquid phosphoric acid with kieselguhr, forming into shapes and calcining. Another portion of the gas oil was charged to theA low temperature conversion step to produce substantial yields of substantially saturated fuel. The temperature was maintained at 750 F. and the pressure at 100 pounds per square inch. A 300 F. end-point gasoline having an octane number of 77 and suitable for use as an aviation base motor fuel was separated. A 3DO-400 F. cut was separated as a side-cut and blended with the olenic gasoline produced in thehigher temperature conversion step to augment the yields of automobile motor gasoline. Minor portions of residual oil suitable for fuel were Withdrawn from both the higher and lower temperature conversion steps. A total yield of 78% of gasoline, including the polymer gasoline produced by polymerization of the olens in the gas, was realized. Approximately 35% of the total yield was aviation base gasoline and the remainder was useful as automobile fuel.

The yields o aviation base fuel could be still further increased-by hydrogenating the Cs cut of the polymers produced, and by charging a regulated amount ci the gasoline produced in the high temperature conversion step to the lov? temperature conversion step, together with the hydrocarbon charging stocir and/or a portion oi the recycle stools. This indicates the advantages or the process because of 'the considerable flexibility of operation made possible.

l claim as my invention:

l. A continuous process for converting hydrom carbon oil into high yields of substantially olefinm free gasone which comprises converting said oil in a plurality oi catalytic conversion stages serially arranged wherein the repeated sequence of steps is carried out at each of said catalytic conversion stages comprisingra primary step ci contacting an olefin-containing gasoline mixed with insuiiciently converted oil produced as hereinafter described, with a cracking catalyst step of partially reactivating said cracking cata@ lyst Vused in said primary and secondary steps with an oxygen-containing gas at a temperature in excess of that used for processing in said primary step, a quaternary step of completing the reactivation of said cracking catalyst with an oxygen-containing'gas while restoring the temperature to that-required for processing in said primary step, maintaining said primary step and said Quaternary step in heat exchange relationship by means of a circulating Iluid heat exchange medium, maintaining said secondary step and saidy tertiary step in heat exchange relationship by means of a separate circulating fluid heat exchange medium, recovering the gasoline from said primary step, recoveringthe gas from said 2,800,033 secondary step, and withdrawing a'minor portion of residue unsuitable for further conversion.

2. A continuous process for converting hydrocarbon oil into high yields of substantially olefinfree gasoline which comprises converting said oil in a plurality of conversion stages serially arranged wherein the repeated sequence of steps is carried out at each of said conversion stages comprising a primary step of contacting said hydrocarbon oil together with an olefin-containing gasoline produced as hereinafter described with a cracking catalyst under conditions of temperature and pressure adequate to effect substantial conversion thereof to substantially oleiinfree gasoline, a secondary step of contacting the insufficiently converted oil from said primary step with said cracking catalyst under conditions of temperature and pressure adequate to effect substantial conversion thereof into olefincontaining gasoline vfor 'conversion in said prix mary step, a tertiary step of partially reactivating said catalyst with an oxygen-containing gas at a temperature in excess of that used in said secondary step, and a quaternary step of completing the reactivation of said cracking catalyst with an oxygen-containing gas while restoring the temperature to that required in said primary step, maintaining those conversion stages operating in said primary and quaternary steps in heat exchange relationship by means of a circulating iluid heat exchange medium, maintaining the conversion stages operating in said secondary and tertiary steps in heat lexchange relationship by means of a separate circulating heat exchange medium, and recovering the gasoline from said primary step.

3. A continuousprocess for converting hydrocarbon oil into high yields of substantially olefin-free gasoline which comprises converting said hydrocarbon oil in a plurality of conversion stages serially arranged wherein the repeated sequence of steps is carried out at each ofsaid conversion stages comprising a primary step of contacting a portion of said hydrocarbon oil mixed with gasoline and insumciently converted oil produced as hereinafter described with a cracking catalyst under conditions of temperature and pressureadequate to eiect substantial conversion thereof to substantially olen-i'ree gasoline, a secondary step of contacting a major portion oi' said hydrocarbon oil with .a cracking catalyst under conditions of temperature and pressure adequate to effect substantial conversion thereof into olefin-containing distillate and insufficiently converted oil for conversion in said primary step, a tertiary step of partially reactivating said cracking catalyst used in said primary and secondary steps with an oxygen-containing gas at a temperature in excess of that used for processing in said primary step, and a quaternary step of completing the reactivation-of said cracking catalyst with an oxygen-containing gas while restoring' the temperature to that required for processing in said primary step, maintaining those conversion stages operating in said primary and quaternary steps in heat exchange relationship by means of a circulating iluid heat exchange medium, maintaining those conversion stages operating in said secondary and tertiary steps in heat exchange relationship by means of a separate circulating fluid heat exchange medium, recovering the gasoline from said primary step and returning a portion of. the insumciently converted oil from said primary step for further conversion.

4. A continuous process for converting hydrocarbon oil into high yields of substantially oleiin-free gasoline which comprises converting said hydrocarbon oil in a plurality of conversion stages serially arranged wherein the repeated sequence of steps is carried out at each of said conversionv stages comprising a primary step of contacting a portion o f said hydrocarbon oil mixed with the olefin-containing reaction products of catalytic cracking produced as hereinafter described with a cracking catalyst under conditions of temperature and pressure adequate to effect substantial conversion thereof to substantially olefin-free gasoline, a secondary step of contacting a portion of said hydrocarbon oil with said. cracking catalyst under conditions of l temperature and pressure adequate to effect substantial conversion thereof into olefin-containing reaction products for conversion in said pri- A and secondary steps with an oxygen-containing gas at a temperature in excess of that requiredl for processing in said primary step, and a quaternary step of completing the reactivation of said cracking catalyst 4with an oxygen-containing gas while restoring the temperature to that required for processing in said primary step, maintaining those conversion stages operating in said primary and quaternary steps in heat exchange relationship by means of a circulating fluid heat exchange medium, maintaining those conversion stages operating in said secondary and tertiary steps in heat exchange relationship by means of a separate circulating fluid heat exchange medium, recovering the gasoline from said primary step and returning a portion of the insufficiently converted oil to said secondary step for further conversion.

5. A continuous process for converting hydrocarbon oil into substantial yields of gasoline which comprises converting said hydrocarbon oilin a plurality of conversion stages serially arranged wherein the repeated sequence of steps d rocarbon oil with a cracking catalyst under conditions of temperature and pressure adequate to eifect substantial conversion thereof into olefincontaining gasoline, the 300 F. end-point fraction of which is converted in said primary step, a tertiary step of partially reactivating said cracking catalyst Whichhas been used in said primary and secondary steps with an oxygencontaining gas at a temperature in excess of that used for processing in said primary step, and a quaternary step of completing the reactivation of said cracking catalyst with an oxygen-containing gas while returning the temperature to that required for processing in said primary step, recovering the gasoline from said primary step, recovering the gas and gasoline from said secondary step and supplying a portion of said gasoline having an end-point of approximately 300 F. to said primary step, recovering afraction boiling above 300 F. and returning a portion of the insuiliciently converted oil to said secondary step.

LOUIS S. KASSEL. 

